In the past, gyroscopes and gyroscopic devices were constructed of relatively large and expensive electromagnetic devices. These electromagnetic devices incorporated coils and position sensors mounted for relatively high speed, continuous rotational movement.
Eventually, micromechanical rate gyros were developed which included components formed by semiconductor processing techniques. While these devices are relatively small and utilize vibrational motion rather than continuous rotary motion, they are relatively insensitive and costly to manufacture.
Generally, the micromechanical rate gyros are constructed with a central mass, which because of the size of the gyro is very small and requires some very heavy material such as gold to provide sufficient mass. The central mass is mounted in a gimbal structure including mutually orthogonal flexible axes, with the mass and gimbal structure generally lying in a common plane. The central mass and inner mounting gimbal are oscillated or vibrated about a first of the orthogonal axes and rotational movement about an axis perpendicular to the common plane produces vibrational movement about the other of the orthogonal axes, due to the Coriolis, or gyroscopic, effect.
The described micromechanical rate gyro has several problems. Specifically, the centrally mounted mass is expensive and difficult to manufacture. It is difficult to achieve a large enough mass to provide sufficient inertia for good sensitivity and this construction reduces sensing capacitor sensitivity. Also, if the mass is offset even slightly within the gimballed mounting a noticeable sensitivity to cross-axis acceleration is produced. Second, the amount of vibrational movement is limited by the fact that the planar constructed gimbal system is mounted adjacent to a planar surface and increasing the distance between the gimbal system and the planar surface substantially increases the size of the device, which reduces sensitivity due to increased capacitor spacing as well as increasing the cost and complexity of construction. Further, by constructing the device so that the input axis is perpendicular to the common plane, the device is limited to a single axis device. Since the device only senses movement about a single axis, three of the devices must be mounted with the input axes in a mutually orthogonal relationship to sense movement in all directions.
To further reduce the size, cost and usefulness of rate gyros, there is a need for micromechanical rate gyros with increased sensitivity, due to increased inertia achieved by an increased distance of movement and/or an increase in effective mass, higher vibration frequency and smaller capacitive plate separation. Further, it would be convenient to sense movement about more than one axis with a single device.